Special Section on Mask Technology for Optical Lithography

Optical vortex masks for via levels

[+] Author Affiliations
Marc D. Levenson

M.D. Levenson Consulting, 19868 Bonnie Ridge Way, Saratoga, California 95070 E-mail: muddle@aol.com

Takeaki (Joe) Ebihara

Canon USA, Incorporated, San Jose, California 95134

Grace Dai

Sigma-Cad, Campbell, California 95008

Yasutaka Morikawa, Naoya Hayashi

Dai Nippon Printing Company, Limited, Kamifukuoka, Japan

Sze Meng Tan

Picarro, Incorporated, Sunnyvale, California 94085

J. Micro/Nanolith. MEMS MOEMS. 3(2), 293-304 (Apr 01, 2004). doi:10.1117/1.1683304
History: Received Aug. 20, 2003; Revised Oct. 24, 2003; Accepted Dec. 12, 2003; Online March 31, 2004
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In an optical vortex, the wavefront spirals like a corkscrew, rather than forming planes or spheres. Since any nonzero optical amplitude must have a well-defined phase, the axis of a vortex is always dark. Printed in negative resist at 248 nm and NA⩾0.63, optical vortices and optical vortex arrays produce contact holes with 64 nm<CD<160 nm (0.2<k1<0.4), depending on exposure dose. Arrays of vortices with kpitch>0.6 can be patterned using a chromeless phase-edge mask composed of rectangles with nominal phases of 0, 90, 180, and 270 deg. Lithography simulation and resist exposures have demonstrated process windows with 10%Elat and ∼400-nm depth of focus (DOF) for 85-nm CDs at 210-nm pitch with σ=0.15, but the developed contacts are somewhat elliptical. No significant surface development has appeared due to phase-edge printing. However, the spacewidth alternation phenomenon familiar from linear chromeless phase-edge lithography does cause small positional errors for vortex vias, and each of the four vortices in the repeating pattern may behave somewhat differently through focus, potentially limiting the common process window. Smaller CDs and pitches are possible with shorter wavelength and larger NA, while larger pitches give rise to larger CDs. At pitch >0.6 μm, the vortices begin to print independently for σ⩾0.3. Such “independent” vortices have a quasi-isofocal dose that gives rise to 110-nm contacts with Elat>14% and DOF >400 nm. In an actual chip design, unwanted vortices and phase step images would be erased from the resist pattern by exposing the wafer with a second, more conventional, bright-field trim mask. Compared to other ways of producing deep subwavelength contacts, the vortex via process reduces the lithography and process control challenges. © 2004 Society of Photo-Optical Instrumentation Engineers.

© 2004 Society of Photo-Optical Instrumentation Engineers

Citation

Marc D. Levenson ; Takeaki (Joe) Ebihara ; Grace Dai ; Yasutaka Morikawa ; Naoya Hayashi, et al.
"Optical vortex masks for via levels", J. Micro/Nanolith. MEMS MOEMS. 3(2), 293-304 (Apr 01, 2004). ; http://dx.doi.org/10.1117/1.1683304


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